Such mixers are already known, and the one described in U.S. Pat. No. 2,203,961 comprises a body whose upper part comprises a cavity divided into two chambers by an elastic membrane having in its center an orifice on whose edge is fastened the upper edge of a vertical register cylinder which slides in a blind hole and which controls the delivery of air and gas which feed the engine. The lower and upper faces of the elastic membrane specified above are respectively in communication by passages with the air intake duct and engine feed duct.
It is understood that the pressure difference existing between the air intake and the mixer outlet is reflected by the same pressure difference on both sides of the membrane and by a deformation of this latter which fixes the height of the register cylinder. This modifies the delivery of injected gas which thus can be made dependent upon the air delivery and the operating conditions of the engine.
However, such mixers exhibit numerous drawbacks which are due particularly to the fact that the gas content of the air/gas mixture introduced into the engine is not adapted to certain operating conditions, such as idling or starting cold, which is reflected, in particular, by changes in consumption with time.
Further, a considerable pressure loss occurs between the air intake and the engine feed, which is reflected, in particular, by a considerable response time.